1. Field of the Invention
The present invention relates to a document processing system having a character printing unit by which a character can be printed on a desired position of a printing medium.
2. Related Background Art
Conventional text processing systems such as word processors, electronic typewriters and the like are constructed so as to easily produce an unnatural or irregular text by designating a control key such as a print position fine feed key to finely move a character printing unit or head to the right and left and to finely move a platen up and down and print a character on a printing medium at a desired position.
For example, if an unnatural text such as a formula f (x)=x.multidot.sin x shown in FIG. 17A is printed using an ordinary print pitch, a relatively large space is placed between the function symbol "f" and the next left parenthesis so that the printed formula is unbalanced as a whole.
In view of this, the conventional system is provided with a print position fine feed key in order to print the left parenthesis "(" at a most suitable position in the formula as shown in FIG. 17B.
However, in a conventional text processing system, the position of the left parenthesis "(" in the formula cannot be displayed to determine if it is at a suitable position, unless it is actually printed out on the printing medium.
Such phenomenon is related to the use of a display unit mounted on such a text processing system. Namely, in a conventional system, character display is controlled in units of one character, and the display position or address of the display unit at which a character pattern of an input character code is displayed, is unambiguously determined based on the address in a memory in which the display information has been stored, and based on the size of character dot pattern. Consequently, the display position of an input character can not be determined finer than one character unit, thus preventing a change in the display position if an input character to be printed is moved at a finer position than one character unit.
If an input character is changed in position, an operator must print it in order to confirm whether the change was actually and correctly performed on the printing medium. Thus, setting an optimum position of a character may cause an operator to have various experiences, misprints, soiled prints, and blanked portions due to the use of correction agent. Such blanked portions often arise in the case where the positions of consecutive characters are to be adjusted because even if a first character is correctly moved, this character and the next character are often blanked to obtain an optimum relative position if the latter is moved erroneously. Very cumbersome correction becomes necessary particularly for small character fonts such as characters printed below a character string. Further, if such correction is necessary, the printing material such as an ink ribbon must be manufactured using a proper material for such correction, resulting in a considerably large continuous cost. Furthermore, the need for such correction results in poor operability of the print position control function.